only one element get stored in kfifo

[chrishell]

I got it. The correct way to pull out a struct from the kfifo, could be:

rc = kfifo_out(&pfops->mymod_fifo, &r_cache1, sizeof(struct 
mymod_data_pkt));

BR Christian



> hello, Im struggle with a simple kfifo. I try to do it dynamicly. For 
> the sake of simplicity I changed the code in a way that everything with 
> the kfifo is done in the open function of my module.
> 
> First of all, I have a struct, in which I store the pointer to that kfifo:
> 
> struct mymod_private_fops {
>      wait_queue_head_t    wait;
>      struct kfifo         mymod_fifo;
> }
> 
> 
> And the struct in which I store my data:
> 
> struct mymod_data_pkt {
>      __u8     mbyte;
>      __u8     smfunc;
>      ktime_t ktime;
>      __u16    len;
>      __u16    sequence;
>      char    devname[32]
>      void    *page;
> };
> 
> 
> this is the open function, which creates the kfifo and stores the 
> pointer to that kfifo for later usage. As I mentioned I simplified the 
> whole thing to have the store operation into the kfifo and the fetch 
> operation, out of the kfifo in one place. Initially I did this in the 
> read and write function.
> 
> static int mymod_open(struct inode *pinode, struct file *pfile)
> {
>      int rc  = 0,
>          len = 0;
> 
>      struct mymod_private_fops pfops;
>      struct mymod_data_pkt w_cache1, w_cache2, w_cache3 r_cache1, 
> r_cache2, r_cache3;
> 
>      pfops = kzalloc(sizeof(struct mymod_private_fops), GFP_KERNEL);
> 
>      if(pfops == NULL)
>          return -ENOMEM;
> 
>      init_waitqueue_head(&pfops->wait);
> 
>      len = LOG_STACK_SIZE * sizeof(struct mymod_data_pkt);
> 
>      rc = kfifo_alloc(&pfops->mymod_fifo, len, GFP_KERNEL);
>      if(rc) {
>          pr_err("kfifo_alloc failed %d", rc);
>          return rc;
>      }
> 
>      if(! kfifo_initialized(&pfops->mymod_fifo)) {
>          pr_err("kfifo initialized");
>      }
> 
>      w_cache1.mbyte = 4;
>      w_cache1.len   = 245;
> 
>      rc = kfifo_in(&pfops->mymod_fifo, &w_cache1, sizeof(struct 
> mymod_data_pkt));
>      pr_err("kfifo_in returns %d", rc);
> 
>      w_cache2.mbyte = 42;
>      w_cache2.len   = 112;
> 
>      rc = kfifo_in(&pfops->mymod_fifo, &w_cache2, sizeof(struct 
> mymod_data_pkt));
>      pr_err("kfifo_in returns %d", rc);
> 
>      w_cache3.mbyte    = 119;
>      w_cache3.len    = 77;
> 
>      rc = kfifo_in(&pfops->mymod_fifo, &w_cache3, sizeof(struct 
> mymod_data_pkt));
>      pr_err("kfifo_in returns %d", rc);
> 
>      rc = kfifo_len(&pfops->mymod_fifo);
>      pr_err("kfifo_len: %d", rc);
> 
>      memset(&r_cache1, 0, sizeof(struct mymod_data_pkt));
> 
>      rc = kfifo_get(&pfops->mymod_fifo, &r_cache1);
>      pr_err("kfifo_get returns %d", rc);
> 
>      pr_err("content of kfifo r_cache1->mbyte: %d", r_cache1.mbyte);
> 
>      memset(&r_cache2, 0, sizeof(struct mymod_data_pkt));
> 
>      rc = kfifo_get(&pfops->mymod_fifo, &r_cache2);
>      pr_err("kfifo_get returns %d", rc);
> 
>      pr_err("content of kfifo r_cache2->mbyte: %d", r_cache2.mbyte);
> 
>      ...
> 
>      pfile->private_data = pfops;
> 
>      ...
> 
> [  108.200977] kfifo_in returns 64
> [  108.200985] kfifo_in returns 64
> [  108.200990] kfifo_in returns 64
> [  108.200993] kfifo_len: 192
> [  108.200997] kfifo_get returns 1
> [  108.201000] content of kfifo r_cache1->mbyte: 4
> [  108.201003] kfifo_get returns 1
> [  108.201006] content of kfifo r_cache2->mbyte: 0
> [  108.201010] kfifo_get returns 1
> [  108.201013] content of kfifo r_cache3->mbyte: 0
> 
> The initialization worked fine, the store operations went properly. Only 
> pulling data out of the kfifo didn't work
>   as expected.
> Only the 1st element was correct, the 2nd and 3rd element was just 0
> 
> Also the size of the struct and the fifo seems to be okay. The struct 
> has the size of 64 (there is some padding within I think) and after 
> inserting 3 elements the kfifo has the size of 192
> 
> Where is the flaw here?
> 
> 
> Thank you in advance
> 
> Best regards Christian
> 
> 
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